Transient Aspects of Rayleigh Flow at Transonic Speeds

Rajarshi Das,Heuy-Dong Kim 한국추진공학회 2015 한국추진공학회 학술대회논문집 Vol.2015 No.11

Development of high speed combustors requires extensive investigation into transonic and supersonic flow under conditions of heat addition. Conventional Rayleigh theory covers this phenomenon but is limited to steady state conditions. In addition, Rayleigh theory falls short of explaining the effects of heat addition at sonic conditions. In this work, effects of heat addition at choking conditions for Rayleigh flow is investigated treating the flow as unsteady and modifying the governing equations suitably. During the study it was observed that, at sonic conditions, the mass flow unexpectedly changes thereby necessitating an overall change in the flow parameters. Taking this anomaly into account, an analytical solution is proposed in the paper for investigating such flows. The primary observations of this analysis are the unsteady fluctuation of the flow properties at sonic conditions.

Numerical Analysis of Turbulent Boundary Layer Suction in Scramjet Inlets

Rajarshi Das,Kwon Hee Lee,Heuy Dong Kim 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5

Proper design of bleed slots to control boundary layer separation in supersonic inlets is of great importance in today’s world of high speed propulsion systems. Multiple performance parameters have to be taken in to account while designing such systems. the effect of flow and geometric parameter on these performance factors is of countless importance for such work. The present work targets to evaluate the effect of geometric parameters of a single bleed slot in a M∞=2.5 flow on individual aerodynamic performance parameters. The investigation is carried out numerically and important performance parameters like total pressure loss and prevention of separation of boundary layer is investigated. The results obtained revealed that slanted slots perform better than perpendicular slots in terms of boundary layer separation and bleed mass flow albeit a little relaxation in the total pressure loss.

Steady and Unsteady Rayleigh Flow with Heat Addition at High Subsonic Mach Numbers

Rajarshi Das,Huey Dong Kim 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

The heat addition process in compressible flows essentially accompanies unsteadiness, but such a time-dependent behavior of the compressible Rayleigh flow has seldom been known to date. In the present study, an analytical study has been performed to investigate the effect of different types of heat transfer to compressible flows at high subsonic Mach numbers. Changes in basic flow properties due to both steady and unsteady heat transfer into a constant area, frictionless duct over different periods of time were solved numerically. Flow Mach number and velocity were observed to increase rapidly as the flow approached sonic conditions. Change in flow enthalpy and temperature were however different showing an increase initially and then reducing in the vicinity of sonic conditions. Once sonic conditions were attained, the trend in change of flow properties changed substantially with decrease in Mach number under further heat transfer. Attainment of sonic state was observed to depend largely on the amount of heat transfer and the initial conditions.

Shear Layer and Wave Structure Over Partially Spanning Cavities

Rajarshi Das,Heuy Don Kim,Job Kurian 한국가시화정보학회 2013 한국가시화정보학회지 Vol.11 No.2

Study of the wave structure and shear layer in the vicinity of a wall mounted cavity is done by time averaged colour schlieren and time resolved instantaneous shadowgraph technique in an M=1.7 flowfield. Effect of change of cavity width on flow structure is investigated by using constant length to depth (L/D) ratio cavity models with varying length to width (L/W) ratio of 0.83 to 4. The time averaged shock wave structure was observed to change with change in cavity width. Dependence of the shock angle at the leading edge on the shear layer width is also evident from the images obtained. Unsteadiness in the flow field in terms of shear layer dynamics and quasi steady nature of shock waves was evident from the images obtained during instantaneous shadowgraph experiments. Apart from the leading and trailing edge shocks, several other waves and flow features were observed. These flow features and the associated physical phenomena are discussed in details and presented in the paper.

Unsteady Flow Characteristics in a Cavity Based Scramjet Combustor

Rajarshi Das,Heuy-Dong Kim(김희동) 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.12

A numerical study on the effect of periodic oscillations generated by wall mounted cavity on supersonic combustion in a model scramjet combustor is investigated. The investigation has been carried out in a two dimensional numerical model where a cavity of length to depth (L/D) ratio of 2 is mounted on one of the walls of the flow channel. Hydrogen is used as fuel and is injected through a 5㎜ wide injector located at the trailing edge wall of the cavity at a fuel-air equivalence ratio of 0.5. Periodicity of pressure oscillations and variation in overall combustion efficiency was observed to be interdependent from the results of the study.

Shear Layer and Wave Structure Over Partially Spanning Cavities

Das, Rajarshi,Kim, Heuy Dong,Kurian, Job The Korean Society of Visualization 2013 한국가시화정보학회지 Vol.11 No.2

Study of the wave structure and shear layer in the vicinity of a wall mounted cavity is done by time averaged colour schlieren and time resolved instantaneous shadowgraph technique in an M=1.7 flowfield. Effect of change of cavity width on flow structure is investigated by using constant length to depth (L/D) ratio cavity models with varying length to width (L/W) ratio of 0.83 to 4. The time averaged shock wave structure was observed to change with change in cavity width. Dependence of the shock angle at the leading edge on the shear layer width is also evident from the images obtained. Unsteadiness in the flow field in terms of shear layer dynamics and quasi steady nature of shock waves was evident from the images obtained during instantaneous shadowgraph experiments. Apart from the leading and trailing edge shocks, several other waves and flow features were observed. These flow features and the associated physical phenomena are discussed in details and presented in the paper.

Three Dimensional Cavities for Supersonic Mixing

Rajarshi Das,Heuydong Kim,Job Kurian 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.5

Effect of wall mounted three dimensional cavities on the mixing of gaseous injectant based on the entrainment of secondary jet into the primary supersonic flow of Mach number 1.7 is studied. Mixing induced by flow unsteadiness and exchange of fluid between the cavity and main stream flow has been investigated. In order to study the influence of the ratio of cavity length to width (L/W) for constant length to depth ratio (L/D) on the fluid dynamic behaviour, three cavities of L/W ratios between 2 and 4 were used in the study. Acoustic oscillations generated from the cavity were observed to have profound impact on mass exchange between the cavity and the freestream flow. These acoustic oscillations which govern the flow unsteadiness were in turn found to be dependent on the L/W ratio of the cavity. Shift in dominant acoustic mode was observed as the L/W ratio was changed from 3 to 4. Entrainment of secondary injected jet into the primary M=1.7 flow was observed to vary with cavity width quantitatively. The trend in this variation depended on the amplitude of acoustic oscillations generated by the cavities.

Computational Study on the Supersonic Cavity based Combustion

Rajarshi Das,Heuydong Kim 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.5

A comparative study with kerosene and hydrogen fuel in a model scramjet combustor has been carried out numerically under both cold flow and hot flow conditions. The effect of the two fuels on the flow field properties for the same fuel air equivalence ratio of 0.5 in a cavity based combustion mechanism at a freestream Mach number of 2.08 has also been probed. The investigation has been carried out in a two dimensional numerical model where a cavity of length to depth (L/D) ratio of 2 is mounted on one of the walls of the flow channel. Changes in total pressure loss, fuel-air mixing and combustion efficiency were investigated for different fuels. Dependency of flow and performance characteristics on fuel properties was clearly evident from the results.

스크램제트 엔진에서의 모드 천이에 관한 수치해석 연구

하정호,Rajarshi Das,폴루소 라덴데,김태호,김희동 한국추진공학회 2017 한국추진공학회지 Vol.21 No.6

In the present study, theoretical and numerical analyses have been carried out to investigate the detailed flow characteristics during the mode transition. The theoretical analysis rearranged the knowledge of gasdynamics and the previous studies, and the numerical analysis has conducted to solve the 2D unsteady compressible Navier-Stokes equations with a fully implicit finite volume scheme. To validate the numerical analysis, the experiment was compared with it. The total temperature at the inlet of isolator and the hydrogen fuel equivalent ratio were changed to investigate their effects on the mode transition phenomenon. As the results, the numerical analysis reproduced well the experiment qualitatively, the increment in the hydrogen fuel equivalent ratio induced the scram-mode to ram-mode transition which is discontinuous with a non-allowable region, and the variation in the total temperature changed the boundary of the mode transition. 본 연구에서는 모드 천이가 발생하는 동안 상세한 유동 특성을 조사하기 위해, 이론분석과 수치해석을 수행하였다. 이론분석은 기존의 기체역학과 종래 보고된 이론식들 재정립하였으며, 수치해석은 2차원 비정상 압축성 Navier-Stokes 방정식을 풀기 위해 fully implicit finite volume scheme을 사용해 수행하였다. 해석의 검증을 위하여 실험 결과와 비교하였다. 격리부 입구 전온도와 수소 연료의 당량비를 변화시키면서 모드 천이에 미치는 영향을 조사하였다. 해석과 실험 결과는 정성적으로 잘 일치하였다. 당량비가 증가하면 스크램제트 모드에서 램제트 모드로 천이가 발생하였다. 이 때, 천이는 당량비에 따라 불연속적으로 나타나며, Non-allowable region이 존재하였다. 한편 격리부 입구에서 전온도의 증가는 모드 천이 경계를 변화시켰다.

Numerical Visualization and Quantification of Flow Oscillations in a Cavity based Combustor

YunSang Kim,Rajarshi Das,Aran Ye,Heuy Dong Kim 한국가시화정보학회 2015 한국가시화정보학회 학술발표대회 논문집 Vol.2015 No.5